Surgical instrument comprising an instrument handle and zero point adjustment

ABSTRACT

The invention relates to a surgical instrument comprising an instrument handle linked to a proximal end portion of a tube shaft to the distal end portion of which an instrument head is linked so as to be bendable, in which instrument head an effector including at least one pivotal engaging element is rotatably supported. The instrument handle has a number of manipulators and/or operating mechanisms for operating the instrument head and/or the effector via gear trains. According to the invention, a clutch which permits a zero point adjustment individual at least over a predetermined pivoting range of the instrument handle is interposed in the gear train effecting the bending motion of the instrument head. The zero point is defined as a relative position of the instrument handle with respect to the tube shaft in which the instrument head adopts a predetermined bending position with respect to the tube shaft.

The present invention relates to a surgical instrument for minimallyinvasive surgery in accordance with the preamble of claim 1.

From DE 100 36 108 a surgical instrument of this generic type is known.It substantially comprises a tube shaft at the one proximal end of whichan instrument handle is arranged by which an instrument head disposed atthe opposed distal end of the tube shaft is operable through geartrains. The instrument head can be pivoted and/or inclined with respectto the tube shaft and moreover holds an effector rotatably supported inthe instrument head in the form of forceps or tongs whose one jaw ispivoted to the effector and is likewise operable by means of theinstrument handle.

In more concrete terms, the gear trains enable at least a first movementof the instrument handle, according to this prior art to be triggered bythe hand rotation of an operator, to be transformed into a rotation ofthe effector at a predetermined transmission ratio with respect to thisoperating movement. Thus it is possible to rotate the effector despitethe relatively restricted motion capacity of a human hand by up to 3000,for instance, and in this way to realize complex motions without havingto change the grip at the handle. Moreover a second motion of theinstrument handle, for instance bending thereof with respect to the tubeshaft, is converted into an inclination motion of the instrument head.

The gear trains provided inside the instrument handle and the tube shaftare designed such that most largely decoupled operation of eachindividual movement of the instrument head and the effector ispermitted. However, such gears are necessarily extremely complex andconsequently also require sufficient assembly space. Moreover a completedeclutch of the individual movements is not fully ensured.

It has also turned out that, especially in the case of a hand rotationfor turning the effector supported in the instrument head, the naturalstructure of the hand and the motions resulting therefrom, i.e.irrespective of whether or not the gear trains of the surgicalinstrument are in fact completely decoupled, at the same time cause aslight bending of the instrument tip and, moreover, a tilting of theentire instrument shaft, which considerably impedes the handling of theinstrument.

In view of this prior art, it is the object of the present invention toprovide a surgical instrument of this generic type in which motions ofan instrument head as well as of an effector can be performed largelyindependently of the natural conditions of a natural hand structure,decoupled from each other via an instrument handle.

This object is achieved by a surgical instrument comprising the featuresaccording to claim 1.

In principle, the individual degrees of freedom as well as the motionranges of a human hand are predetermined in a restricted range due toits structure and individually deviate only slightly from each other.The use of a generic surgical instrument frequently cannot takerestrictions of the human hand in terms of kinematics intoconsideration, however. In other words, an optimum use of the surgicalinstrument requires a position of the hand or of the surgeon which mightbe unnatural. This entails the fact that such positions cannot bemaintained for a long time or only with great expenditure of force sothat moreover in such positions it is very difficult to work exactlywith the surgical instrument.

Based on these considerations, the core of the invention now consists inpivotally connecting the instrument handle to the tube shaft via aclutch or, more precisely, in interposing a clutch into the gear trainfor transmitting a swivel motion of the instrument handle to theinstrument head for bending the same, which clutch permits an individualzero point adjustment at least in a predetermined range, wherein thezero point is a relative position of the instrument handle with respectto the tube shaft in which the instrument head adopts a predeterminedbending position, preferably the maximum or minimum bending position(stop position) with respect to the tube shaft.

By this technical measure the instrument handle and/or the relativeposition thereof with respect to the tube shaft can be aligned inresponse to the application position of the instrument so that thesurgeon is substantially able to grasp and operate the instrument handlesubstantially within the natural motion range of his hand. Thus, thesurgical instrument according to the invention makes it possible to doprecise work without getting tired.

It is advantageous to design the clutch to be automaticallydisconnecting. I.e. such a clutch is automatically disconnected when apredetermined torque is exceeded and/or transmits only thispredetermined torque and above that it begins to slip.

It is an advantageous possibility of a constructional configuration ofan automatically disconnecting clutch to design a slipping clutch whichbasically provides two torque transmission elements forced against eachother which slip off each other from a defined torque. Specifically, thetorque transmission elements are biased against each other so that theyare adapted to transmit a torque within the scope of a conventional useof the instrument by corresponding frictional contact, which torque isexceeded by further pivoting of the instrument head and thus therelative position of both torque transmission elements is varied,however, in case that the instrument head is in its maximum or minimumbending stop position.

As an alternative, it is also possible, of course, to manually disengagetwo torque transmission elements of the clutch for a zero pointadjustment, wherein in this case it must be ensured, however, that thepredetermined position of the instrument head is observed for awell-directed adjustment of the zero point.

As a further alternative for an automatically disconnecting clutch, alsoan engaging element, for instance in the form of at least one drivingtooth or at least one ball, may be provided which is supported on one ofthe torque transmission elements and is biased against the other torquetransmission element and engages in a recess or undercut. Hereby apositive fit connection is provided which is released upon exceeding atorque defined by the spring bias and the two torque transmissionelements are twisting relative to each other.

Another advantageous configuration of the invention provides to arrangethe clutch in the area of the link point between the instrument handleand the tube shaft. This has the advantage that when dimensioning theclutch there are fewer spatial restrictions, because this section of theinstrument is basically always disposed outside the body to be operatedand moreover for safe handling this area is designed to be large anywayin accordance with the dimensions of a human hand.

Further advantageous configurations of the invention are the subjectmatter of the subclaims.

Hereinafter the invention will be shown in detail by way of a preferredembodiment with reference to the accompanying drawings.

FIG. 1 shows a perspective view of a surgical instrument according to apreferred embodiment of the invention,

FIG. 2 shows a first gear train for pivoting an instrument head by meansof an instrument handle as well as especially a zero point adjustingdevice in the linking area of the instrument handle,

FIG. 3 shows a partial section of the first gear train in the pivotingarea of the instrument head,

FIG. 4 shows a second gear train for a rotation of the instrument headby means of the instrument handle,

FIG. 5 shows a partial section of the second gear train in the pivotingarea of the instrument head, and

FIGS. 6 a-6 c show sectional views of a third gear train in the pivotingarea of the instrument head for actuating forceps supported on theinstrument head.

In FIG. 1 a complete surgical instrument according to a preferredembodiment of the invention is shown in a perspective view. The surgicalinstrument according to the invention consequently includes amulti-functional instrument handle 1 arranged at a proximal end or endportion of a tube shaft 2 preferably made of stainless steel, a steelalloy or a plastics material as well as an instrument head 4 equipped oradapted to be equipped with an effector 3 which is provided at theother, distal end of the tube shaft 2.

In general, the instrument head 4 is supported on the respective end ofthe tube shaft so that it can be pivoted or bent with respect to thetube shaft 2, whereas the effector 3 can be rotated in each bendingposition of the instrument head 4 about the longitudinal axis thereof,the two above-mentioned motions being adapted to be performed by meansof the instrument handle 1. To this effect, a number of manipulatorsand/or operating mechanisms are provided at the instrument handle 1which are operatively connected via appropriate gear trains providedinside the instrument handle 1 and the tube shaft 2 to the instrumenthead 4 and the effector 3, respectively, so as to be able to perform theindividual movements of the instrument head 4 and the effector 3independently of each other, i.e. in a decoupled manner.

Specifically, the instrument handle 1 consists of an ergonomicallyshaped handle member 5 which is mounted in a pivoting and inclinablemanner to the tube shaft 2 and on which a first manipulator 6, in thepresent case preferably in the form of a turning knob, and a secondmanipulator 7, in the present case preferably in the form of a handlelever, are supported. Thus, the instrument handle 1 according to thepreferred embodiment of the present invention comprises a total of threeoperating mechanisms for three independent movements of the and [sic] onthe instrument head 4, respectively. It is explicitly emphasized in thiscontext that the instrument handle 1 may also have fewer operationpossibilities, for instance only one operating mechanism, respectively,for pivoting the instrument head 4 and rotating the effector 3.

The exterior structure of the instrument handle 1, especially withrespect to the operating mechanism for pivoting and bending theinstrument head 4 and with respect to the corresponding bending geartrain is shown in FIGS. 2 and 3.

The handle member 5 schematically shown in FIG. 2 is pivotally connectedto the tube shaft 2 via a crank member 8 which is connected to thehandle member 5 through a clutch 7 further described hereinafter and hasthe form of a rotary shaft or rotary disk. The rotary shaft 8 ispreferably aligned so as to be perpendicular to the tube shaft 2 as wellas to the handle member 5 and spaces the handle member 5 from the tubeshaft 2 such that the latter can be pivoted substantially in parallel tothe tube shaft 2 past the same.

At the handle member 5 itself, a kind of tube or sleeve-shapedconnecting base 39 is fastened to the proximal end portion thereof whichextends substantially perpendicularly, i.e. in a radial direction awayfrom the handle member 5. The tubular connecting base 39 includes at itsfree end an outer sliding face (not shown in detail) onto which an openlock washer 38 is placed under stress.

The rotary shaft 8 is rotatably placed on the connecting base 39 at itsend portion facing the handle member 5. To this end, the rotary shaft 8is bored open at the inside over a predetermined axial length to aninner diameter which is so much larger than the outer diameter of theconnecting base 39 that at least a clearance fit is provided between thesame and the rotary shaft 8. Hereby a circumferential surface having apredetermined radius is formed at the bored open inner wall of therotary shaft 8, with a radially extending pin 40 which is insertedthrough a radial through bore from the sheath side of the rotary shaftto the inside projecting therefrom.

When assembling the rotary shaft 8 it is attached to the connecting base39 until the lock washer 38 is positioned on or at the innercircumferential sliding face of the rotary shaft 8. The pin 40 projectsinto the radial gap formed by the open lock washer 38 and thus makes apositive fit connection between the rotary shaft 8 and the lock washer38 which, in turn, forms a frictional engagement with the connectingbase 39. It is explicitly pointed out in this context that the foregoingclutch may also be designed in an inverse manner in terms of kinematics,i.e. the lock washer 38 may be provided in the rotary shaft 8 byfrictional engagement and may enter into a positive fit connection witha pin which is inserted in the connecting piece.

If the instrument handle 1 is now pivoted about its pivot axis(corresponding to the central axis of the rotary shaft 8), the pivotingmotion is transmitted via the lock washer 38 seated on thecircumferential sliding face of the connecting base 39 or on the rotaryshaft 8 by frictional engagement to the pin 40 projecting into the lockwasher gap and thus to the rotary shaft 8 or the connecting piece 39which consequently rotates integrally with the instrument handle 1. Themaximum torque to be transmitted is defined by the biasing force bywhich the lock washer 38 is placed onto the circumferential slidingface. As soon as this torque has been exceeded, the lock washer 38starts sliding on the circumferential sliding face, whereby the relativeposition of rotation between the instrument handle 1 and the rotaryshaft 8 is varying.

In this context, it is referred to the fact that the lock washer 38 ofcourse may also be caught in respective circumferential guides, forinstance in the form of inner and/or outer grooves provided at therotary shaft 8 and/or the connecting base 39 so as to have an axialguiding.

The rotary shaft 8 forming a central through passage 9 for accommodatinggear members, which will be described hereinafter, is designed on itsone front facing the tube shaft 2 to include a crank guide 10 in theform of a cam-shaped groove in which a driving pin 11 engages which isfastened to an axially movable pushing tube 12 supported in a tube shaft2. The groove 10 is formed such that during a motion of rotation of therotary shaft 8 by appropriately pivoting the handle member 1 the drivingpin 11 slides along the groove 10 and, in so doing, performs a forcedcompensating motion in the longitudinal direction of the tube shaft 2which is transmitted to the pushing tube 12 and, depending on thedirection of rotation of the rotary shaft 8, results in a reciprocatingmovement of the pushing tube 12 inside the tube shaft 2.

The above-described structure is finally held together by a hub in theform of a hub bolt (not shown in detail) which is fixed to the tubeshaft and penetrates the rotary shaft 8 as well as the handle member 5in the pivot axis thereof and is fixed by a nut likewise not shown indetail.

The distal end portion of the pushing tube 12 opposed to the crankmember 8 is designed to include a longitudinal extending mounting link13 projecting from the distal end of the pushing tube 12 and forming ahinge and/or hinge eyes 14 at its free end portion. Moreover the frontof the tube shaft 2 is beveled at its distal end portion at an angle ofpreferably 45° and is formed to include lateral link eyes 15 to whichthe instrument head 4 is pivotally linked via pivot pins. The samelikewise consists of a tube member 16 whose one front at which controleyes 17 are formed for the connection to the tube shaft 2 and the linkeyes 15 thereof is equally beveled at an angle of preferably 45°, namelysuch that after linking the instrument head 4 to the tube shaft 2 thetwo aforementioned bevels are complementary and enable the tube member16 to bend with respect to the tube shaft 2 by about 90°, preferably70°.

Moreover a hinge and/or hinge eyes 18 is/are formed at the beveled frontof the tube member 16. To the hinge eyes 14; 18 provided on the pushingtube side and on the tube member side a rocking lever 19 is hinged whichis consequently offset radially outwardly with respect to the pivot axisof the instrument head 4 and transmits an axial translational motion ofthe pushing tube 12 to the tube member 16, whereby the latter is pivotedabout its pivot axis.

Hereinafter, by way of the FIGS. 4 and 5 the operating mechanism for arotation of the effector 3 supported in the instrument head 4 as well asthe corresponding rotation gear train are described.

As one can further take from FIG. 2, the above-mentioned tube member 16of the instrument head 4 simultaneously constitutes a casing and/or areceptacle for the effector 3. Irrespective of which type of effectorthis is, i.e. irrespective of whether for instance a needle holder,tongs, forceps or scissors are used as effector, the latter has apreferably hollow rotational axis 20 which is rotatably inserted in thetube member 16 of the instrument head 4 and is secured against an axialmovement. The length of this rotational axis 20 is selected so that itends approximately in the area of the pivot axis of the instrument head4 and is provided at its free end projecting toward this pivot axis withan output spur gear 21 which is mounted on the rotational axis 20 of theeffector 3 in a torque-proof manner. Especially in FIG. 2 the pivot axisof the instrument head 4 is shown by a broken line through the eyes 15.

As one can further take from FIG. 5, on the pivot axis of the instrumenthead 4 a torque transmission spur gear 22 is provided which is pivotedto one of the two pivoting pins of the instrument head 4 not shown indetail, which form the pivot axis shown in an idealized way, and is inmesh with the output spur gear 21. The torque transmission spur gear 22,in turn, is in mesh with a drive spur gear 23 that is mounted in atorque-proof manner on a drive shaft 24 rotatably guided inside thepushing tube 12 (not shown in FIGS. 4 and 5), as it is especially shownin FIG. 4. At the end of the drive shaft 24 opposing the drive spur gear23 a further torque initiating spur gear 25 is arranged in atorque-proof manner, according to FIG. 4, which is in mesh with along-face pinion 26 supported in the central through passage 9 formedinside the crank member 8.

The crank member 8 is not shown in FIG. 4.

Ultimately, the long-face pinion 26 is in mesh with an actuating shaft27 and a spur gear 28 attached thereto inside the handle member 5, theactuating shaft being fixedly connected to the one manipulator, theturning knob 6 in the present case.

As one can take especially from FIG. 4, the turning knob 6 forms thedistal tip or the outer end of the instrument handle 1. It is fixedlyconnected to the actuating shaft 27 extending substantially along thelongitudinal axis of the handle member 5. The turning knob 6 includes arear edge portion facing the handle member 5 schematically shown assleeve in FIG. 4 which edge portion is sliding adjacent to the handlemember 5 and thus seals the handle member 5 at its distal end.

When actuating the turning knob 6 the motion of rotation thereof istransmitted via the actuating shaft 27 inside the handle member 5, thelong-face pinion 26, the connected driving shaft 24 inside the pushingtube 12 as well as the transmission spur gear 22 to the effector 3 andthe latter is rotated. The turning knob 6 is advantageously operated bythe fingers, especially by the thumb and the index, of the operator'shand, while the handle member 5 is held in hand. Thus it is possible togenerate any rotation at the effector 3 without the operator having tochange his grip at the handle member 5. The fingers of a human hand areadapted to work in a fine-motor way and also the finger tips areprovided with a plurality of nerve endings permitting a distinct tactilefeeling. Accordingly, motions which require high accuracy should beperformed by the fingers. It has turned out that the rotation of theeffector 3 is such a motion and therefore, according to the invention,is triggered by the turning knob 6 without a motion being transmitted tothe tube shaft 2 by advantageously turning the knob 6 for a rotation ofthe effector 3. Rather, the operator's hand can be maintained steady.

It is furthermore pointed out in this context that the driving shaft 24and the pushing tube 12 are supported to be movable in axial directionrelative to each other. I.e., rotation of the crank member 8 triggeredby pivoting the instrument handle 1 does cause a translational motion ofthe pushing tube 12, yet, at the same time, the driving shaft 24 is heldin position, i.e. in mesh with the long-face pinion 26, thereby thepushing tube 12 performing an axial movement relative to the tube shaft2 as well as to the driving shaft 24.

Finally hereinafter the operating mechanism for the effector 3, i.e. thefunctions thereof and the corresponding effector gear train aredescribed by way of the FIGS. 5 and 6 a-6 c.

In accordance with FIG. 5, in the present embodiment of the inventionthe effector 3 is designed as tongs having one fixed jaw 29 and onemovable, i.e. pivotal jaw 30. The fixed jaw 29 forms a unit togetherwith the rotary shaft 20 of the effector 3 and is preferably designedintegrally with the rotary shaft 20, whereas the movable jaw 30 islinked to the fixed jaw 29 to be pivotal at one end.

The movable jaw 30 forms a linking point 31 for a push pin 32 which issupported inside the rotary shaft 20 so as to be relatively movable sothat by axial displacement thereof a pivotal motion of the movable jaw30 with a maximum possible transmission is caused. As particularly shownin FIG. 6 a-6 c, the push pin 32 is axially biased by a spring 33 in theopening direction of the tongs enclosing the push pin 32 inside therotary shaft 20. For this purpose, the push pin 32 forms a shaftprotrusion on which the biasing spring 33 is supported at its one end.The other end of the biasing spring 33 is supported against the fixedjaw 29 of the tongs. An end piece 34 of the push pin 32 projecting fromthe rotary shaft 20 in the direction of the pivot axis of the instrumenthead 4 has a ball-shaped head, the radius of the ball-shaped head 34 inthe present case preferably being about 2.5 mm.

The aforementioned drive shaft 24 for rotationally driving the effector3 supported in the instrument head 4 is provided with a substantiallycontinuous axial bore (not shown in detail). In this axial bore, apushing bar 35 is guided to be axially movable as well as rotatablyguided relative to the drive shaft 24, the front face of the pushing barfacing the pushing pin 32 being chamfered corresponding to the chamfersof the distal front faces provided at the tube shaft side and thepushing tube side, i.e. preferably 45° in the same direction. Thepushing pin 32 is biased against this chamfered front face of thepushing bar 35 by the spring 33 and abuts against the same. The contactface between the pushing bar 35 and the pushing pin 32 is substantiallypunctiform due to the afore-described ball-shaped head of the pin 32,namely independently of the degree of bending of the instrument head 4and independently of the position of rotation of the effector 3.

As can be seen from FIG. 6 a, the pushing pin 32 as well as the pushingbar 35 are aligned axially with respect to each other in case that thebending of the instrument head 4 with respect to the tube shaft 2 issubstantially 0°. Moreover, in this position of the instrument head 4,the pushing pin 32 is positioned such that the center of the ball-shapedhead 34 of the pushing pin 32 is located approximately in the pivot axisof the instrument head 4.

At its proximal end, the pushing bar 35 is connected via a gearmechanism 36, not shown in detail, to the actuating lever 7 which ispivoted to the handle member 5, as already briefly explained at thebeginning of this description.

The functioning of the surgical instrument according to the inventionwill be described hereinafter in detail.

Rotation of the effector 3 supported in the instrument head 4 iseffected by actuating the turning knob 6 supported at one end of thehandle member 5, wherein, as explained already in the foregoing, theturning knob 6 can be turned about its axis of rotation so far that arotation of approx. 360° is realized at the effector 3 without the gripat the handle member 5 necessarily having to be changed. This motion ofrotation is transmitted via the actuating shaft 27 to the long-facepinion 26 which, in its turn, transmits its rotation to the drive shaft24 extending inside the pushing tube 12. The motion of rotation of thedrive shaft 24 causes a rotation of the transmission spur gear 22 whichquasi bridges the pivot axis of the instrument head 4 and thus triggersa motion of rotation of the effector 3 inside the tube member 16 of theinstrument head 4 about the tube member axis.

According to the present embodiment, the entire handle member 5 has tobe pivoted about the longitudinal axis of the crank member and therotary shaft, respectively, to effect a bending, i.e. a pivotingmovement of the instrument head 4 and, thus, of the effector 3. In otherwords, a pivoting movement of the handle member 5 with respect to thetube shaft 2 causes a rotation of the crank member 8 connected to thehandle member 1 by frictional engagement in the direction of rotationvia the clutch 37. At the same time, however, the long-face pinion 26 isrotated along with the crank member 8 due to the fact that a kind ofautomatic lock by friction (efficiency of the gear) occurs by the meshengagement between the actuating shaft 27 and the long-face pinion 26,said lock being possibly further assisted by slightly holding theactuating knob 6 and by the static friction between the actuating knob 6and the handle member 5.

The rotation of the crank member 8 is transmitted via the crank orrather groove 10 at the front of the member 8 as well as the driving pin11 into an axial movement of the pushing tube 12, which is transformedvia the hinged rocking lever 19 into a pivoting movement of theinstrument head 4 about the pivot axis thereof. However, this pivotingmovement is automatically also performed by the output spur gear 21which is fixed to the rotational axis of the effector 3 and is in meshwith the transmission spur gear 22. If, accordingly, the transmissionspur gear 22 were stationary in this kind of operation, i.e. thepivoting operation, the pivoting movement of the instrument head 4 wouldcause the output spur gear 21 to roll off the transmission spur gear 22in the same direction and, thus, would inevitably result in asuperimposed motion of rotation of the effector 3.

As described in the foregoing, however, the long-face pinion 26 isrotated along with the crank member 8 during a pivoting movement of thehandle member 5 and thus drives the drive shaft 24 inside the pushingtube 12. The transmission ratio between the long-face pinion 26 and thedrive shaft 24 is calculated such that the transmission gear 22 isrotated by the drive shaft 24 about such an angle of rotationcorresponding to the angle of rotation which is caused by the outputgear 21 during a corresponding bending of the instrument head 4, wherebyboth rotations compensate each other due to their counter-rotation. Inthis constellation the relative position between the transmission spurgear 22 and the output spur gear 21 is maintained even during thebending motion of the instrument head 4 so that the effector 3 is heldin each bending position of the instrument head 4 and during a bendingmotion, respectively, in its current position of rotation with respectto the instrument head 4.

As already stated in the foregoing, the clutch 37 in the present caseprovided in the form of a slipping clutch can only transmit apredetermined maximum torque. This maximum torque is selected such thatit cannot be exceeded during normal use of the instrument. The maximumbending position as well as the maximum expanding position of theinstrument head 4 is defined by a stop mechanism of the hinge betweenthe instrument head 4 and the tube shaft 2, as described in theforegoing already. As soon as the instrument head 4 has reached thesepositions, a further bending of the instrument head 4 to the respectivedirection is no longer possible.

This constructional configuration can be advantageously used for anadjustment of the relative position of the handle member 5 to bepredetermined with respect to the tube shaft 2, or rather for zero pointadjustment as it is called. For this purpose, the instrument head 4 isbent in one or the other maximum stop position. After reaching therespective stop position the operator exerts an additional pivotingforce upon the instrument handle 1 until the torque resulting herefromexceeds the maximum torque of the clutch 37 to be transmitted. In thismoment the connecting base 39 slides off inside the rotary shaft 8,whereby the original angle position of the instrument handle 1 relativeto the tube shaft 2 changes for the selected maximum stop position ofthe instrument head 4.

In order to effect the operation of the effector 3, i.e. the functionthereof, the lever 7 pivoted to the handle member 5 is provided in thepresent preferred embodiment. As already described in the foregoingconcerning FIGS. 6 a-6 c, lever 7 is operatively connected via areversing gear not shown in detail or an appropriate joint mechanism tothe pushing rod 35 which is supported in the rotary shaft 24 and whichaxially reciprocates relative to the rotary shaft 24 upon acorresponding operation of the lever 7. A simple Bowden cable ordeflecting lever would also be conceivable for a power transmission tothe pushing rod 35.

FIG. 6 a shows the relative position of the pushing rod 35 and thepushing pin 32 in a bending position of the instrument head 4 of 0° withthe tongs being opened, FIG. 6 b shows the relative position of thepushing rod 35 and the pushing pin 32 in a bending position of theinstrument head 4 of approx. 45° with the tongs being opened, and FIG. 6c shows the relative position of the pushing rod 35 and the pushing pin32 in a bending position of the instrument head 4 of approx. 45° withthe tongs being closed.

As one can take from FIGS. 6 a-6 c, the pushing pin 32 is kept inconstant contact with the beveled or chamfered distal front of thepushing rod 35 by the biasing force of the spring 33. When the pushingrod 35 is displaced in the direction of the instrument head 4 in thecase of a 0° bending of the instrument head 4 according to FIG. 6 a, thepushing pin 32 is displaced at the same speed and over the same distanceas the pushing rod 35, i.e. without transmission, against the biasingforce of the spring 33, whereby the jaw 30 of the tongs linked theretois pivoted in the closing direction.

In this context, it is referred to the fact that by the displacingaction of the pushing rod 35, the pushing pin 32, i.e. especially thecenter of the pin head radius, remains only approximately on the pivotaxis of the instrument head 4, i.e. it moves in a kind of orbit during abending motion of the instrument head 4. As already explained in thebeginning of the description of figures, however, the regulatingdistances for opening and closing the tongs, for instance, are so smalldue to the set transmission rates that the orbit radius can becalculated theoretically, but it has no relevant influence on theposition of the tongs for reasons of manufacture already (naturalelasticity of the materials used, dimensional tolerances and play at thelink joints and gear parts). In other words, the position of the tongsis determined by the position of the lever 7 which, in its turn, is heldby an operator and thus is subjected, for instance, to non-controllablemotions of the hand (trembling motions). Such disturbances produced dueto manual operations are greater by far and, therefore, practically onlyrelevant compared to the disturbances produced by the afore-describedorbit motion.

That is to say, irrespective of the current position of the pushing rod35 and the pushing pin 32, respectively, a bending of the instrumenthead 4 does generally not only cause the pushing pin 32 to pivot withrespect to the pushing rod 35 but also causes the pin head 34 toslightly slide off the chamfered front of the pushing rod 35. By thislittle slide-off motion, the bearing contact of the pushing pin 32 withthe front is maintained, wherein only such compensating longitudinalmotion of the pushing pin 32 takes place as a result of its slide-offmotion, however, which entails no practically relevant change of theclosing or opening position at the effector 3. At the same time,however, some power deflection mechanism is provided so as to bringabout a longitudinal motion of the pushing rod 35 into a longitudinalmotion of the pushing pin 32 now provided at an angular position withrespect to the pushing rod 35 by the beveling of the front of thepushing rod.

In other words, if the pushing rod 35 is displaced in a bendingposition >0° according to FIG. 6 b in the closing direction of theeffector 3, as illustrated in FIG. 6 c, the chamfered front of thepushing rod 35 slides longitudinally past the pin head 34 and thusexerts an advance force on the pushing pin 32 which accordingly moves inthe closing direction of the effector 3.

1. A surgical instrument comprising an instrument handle linked to aproximal end portion of a tube shaft, and at a distal end portion of thetube shaft, an instrument head is linked so as to be bendable, theinstrument head has an effector including at least one pivotal engagingelement that is rotatably supported, wherein said instrument handle hasa number of manipulators and/or operating mechanisms for operating saidinstrument head and/or said effector via gear trains, wherein a clutchwhich permits an individual zero point adjustment at least over apredetermined pivoting range of said instrument handle is interposed ina gear train effecting the bending motion of said instrument head,wherein the zero point is a relative position of said instrument handlewith respect to said tube shaft in which said instrument head adopts apredetermined bending position with respect to said tube shaft.
 2. Asurgical instrument according to claim 1, characterized in that thepredetermined bending position is the maximum or minimum bendingposition of said instrument head.
 3. A surgical instrument according toclaim 1, characterized in that said clutch is a slipping clutch having apredetermined maximum transmittable torque.
 4. A surgical instrumentaccording to claim 2, characterized in that said clutch is a slippingclutch having a predetermined maximum transmittable torque.
 5. Asurgical instrument according to claim 2, characterized in that saidclutch is arranged in the linking area between said instrument handleand said tube shaft.
 6. A surgical instrument according to claim 3,characterized in that said clutch is arranged in the linking areabetween said instrument handle and said tube shaft.
 7. A surgicalinstrument comprising an instrument handle linked to a proximal endportion of a tube shaft, and at a distal end portion of the tube shaft,an instrument head linked so as to be bendable, the instrument headhaving an effector including at least one pivotal engaging element thatis rotatably supported, wherein said instrument handle has a number ofat least one selected from the group consisting of manipulators andoperating mechanisms for operating at least one selected from the groupconsisting of said instrument head and said effector via gear trains,wherein a clutch which permits an individual zero point adjustment atleast over a predetermined pivoting range of said instrument handle isinterposed in a gear train effecting the bending motion of saidinstrument head, wherein the zero point is a relative position of saidinstrument handle with respect to said tube shaft in which saidinstrument head adopts a predetermined bending position with respect tosaid tube shaft, and said clutch being arranged in the linking areabetween said instrument handle and said tube shaft.